1. Field of Invention
The present invention relates to waterborne polyurethane with a reactive functional group and a nanocomposite based on the waterborne polyurethane and, more particularly, to waterborne polyurethane with a reactive side-chain group and clay based on the waterborne polyurethane and, more particularly, to waterborne polyurethane added with a small molecular monomer with a reactive functional group to increase the molecular weight and enhance the physical strength, the chemical resistance, the mechanical strength, the hydrolysis resistance, the thermo-tolerance and wear resistance.
2. Related Prior Art
Waterborne polyurethane has been developed for about 60 years and commercialized for more than 30 years. Conventionally, to make waterborne polyurethane, polyol and a hydrophilic functional alcohol (or amine) monomer are pre-polymerized in a small amount of hydrophilic solvent and an excessive amount of di-isocyanate, and neutralized by an ionized compound. The hydrophilic solvent may be N-methyl pyrrolidone (“NMP”), methyl ethyl ketone (“MEK”) or acetone. The ionized compound may be carboxylic group/tertiary amine or sodium salt. Thus, the pre-polymer of the polyurethane is ionized. As a molecular chain grows to a certain length, the activity of the terminal isocyanate is considerably reduced. Hydrophilic amine can be used to extend the molecular chain and then enlarge the molecular weight, thus producing waterborne polyurethane dispersion.
Early patents related to waterborne polyurethane are mostly focused on processes for making waterborne polyurethane. Recent patents related to waterborne polyurethane are mostly focused on improvement of the physical properties of waterborne polyurethane and applications of waterborne polyurethane. In Taiwanese Patent Nos. 293962 and 262197, waterborne polyurethane dispersion is disclosed for coating, adhering and gluing glass fibers. in Taiwanese Patent No. 228515, polyurethane, polyurethane-polyurea or polyurea dispersion that is self-crosslink at high temperature is used as paste for glass fibers so that the finished glass fibers exhibit improved processability and that plastics enhanced by the glass fibers exhibit improved mechanical properties. In Taiwanese Patent No. 191177, a di-isocyanate uretedione derivative is disclosed for use in waterborne polyurethane. The di-isocyanate uretedione derivative is made by addition aziridine in di-isocyanate uretedione.
The physical properties of waterborne polyurethane can be enhanced by a reactive design. For example, disclosed in Taiwanese Patent No. 225495 is polyurethane dispersion of reactive or post-crosslink polyurethane. In Taiwanese Patent No. 197134, there is disclosed waterborne polyurethane lotion and a related coating. Moreover, waterborne polyurethane dispersion derived from blocked aromatic diisocyanate has been disclosed in papers such as U.S. Pat. No. 4,387,181 and Progress in Organic Coatings, 48, 2003, 71-79.
In Taiwanese Patent No. 176144, disclosed waterborne polyurethane dispersion. When the temperature reaches a certain degree, isocyanate will be produced and reacts with any substance that contains the hydroxyl group. Such blocked waterborne polyurethane can be used in textile and on wood, paper and plastics.
However, to effectively emulsify and disperse the pre-polymer in water, a practical product must include aliphatic or cycloaliphatic di-isocyanate that is lowly water-reactive such as di-isocyanate (“IPDI”), hexamethylene diisocyanate (“HDI”) and bis(cyclohexyl)methylene diisocyanate (“H12MDI”). These compounds are expensive, and their physical properties are no match of solvent-type counterparts because of the structure of aliphatic compounds.
However, many organic solvents are used currently such as toluene and dimethylformamide (“DMF”). These compounds pollute the environment and impose hazard to human health. As the environmental protection is getting more attention worldwide and laws and rules are getting tougher against environmental pollution, there is a growing need for low-pollutant and high-performance waterborne resin.
To solve the foregoing problems, conventionally, aliphatic or cycloaliphatic di-isocyanate is used at the ends of polyurethane pre-polymer to suppress reaction of the functional group (“NCO”) with water in dispersion and therefore slow down the reduction of the NCO and avoid failure of dispersion. Related techniques can be found in U.S. Pat. Nos. 7,193,011, 5,714,561, 5,852,105 and 5,905,113, U.S. Patent Application Publication No. 2009/0192283 A1, and European Patent Nos. 738,750 and 682,049.
In Journal of Polymer Science: Part A: Polymer Chemistry, 2004, 42, 4353-4369, disclosed waterborne polyurethane as methylene di-p-phenyl diisocyanate (“MDI”)/IPDI mixture. The intermolecular forces and physical properties in relation to different concentrations of MDI have been discussed.
Disclosed in U.S. Patent Application Publication Nos. 2003/0027923 A1 and 2005/0020707 A1 is high-performance waterborne polyurethane. Reaction of the functional group (“NCO”) of the aliphatic or cycloaliphatic di-isocyanate with water in dispersion suppress and therefore slow down the reduction of the NCO and avoid failure of dispersion. In the dispersion of prepolymer with aromatic isocyanate as a terminal group, reaction of the functional group of isocyanate with water is suppressed and the molecular chain is effectively extended. Toluene diisocyanate (“TDI”) is used as an initiator without having to use any aliphatic or cycloaliphatic di-isocyanate. By strict control over the concentration of the functional group of NCO in the prepolymerization and the concentration of a chain-extending agent, waterborne polyurethane dispersion is made with excellent physical properties and stability in storage.
Except addition of a curing agent and changing the properties of the components, waterborne polyurethane nanocomposites have been widely studied, e.g., Macromolecules, 2006, 39, 6133 and Journal of Polymer Science: Part A: Polymer Chemistry, 2006, 44, 5801. Clay is lamination of silicate layers and an abundant, inexpensive inorganic material in the nature. Clay exhibits advantages such as excellent mechanical properties, thermo-tolerance, chemical resistance and a low expansion coefficient, and therefore is often used as an enhancing material for polymers. However, unmodified clay is hydrophilic and poorly compatible with polymers that are hydrophobic, and the silicate layers tend to be aggregated and cannot be evenly distributed. However, the clay is hydrophilic in nature and lacks the affinity for hydrophobic organic polymers. To improve its miscibility with polymers, the clay must be modified to become organophilic by widening the interlayer spacing with surfactants. In 1987, Toyota released a nanometer dispersed clay/nylon nanocomposite the first time. Since then, there have been some patents related to nanometer clay/waterborne polyurethane composites. In Taiwanese Patent No. 230181 for example, a method is disclosed for making waterborne polyurethane/clay nanocomposites. C6˜C18 alkyl diamine are used to modify clay, the modified clay is used with waterborne polyurethane to form a pre-polymer, and they form a stable dispersion after the molecular chain is extended.
In Taiwanese Patent No. 263628 for example, a method is disclosed for making modified clay and polyurethane resin/clay nanocomposites. A lipophilic modifier and a reactive modifier of a structure that includes —OH and —NH are used. The reactive modifier includes a functional group for reacting with polyurethane resin. The gallery between two adjacent layers of the modified clay is increased to 14.6 to 60 Å. In the composites and dispersion, the gallery between two adjacent layers of the modified clay can be increased by 5 to 10 Å, and the tensile strength and wear-resistance are increased.
In Taiwanese Patent No. 165322, a method is disclosed for modifying clay by a multi-functional organic material and an elastic nanometer clay/polyurethane composite made of polyurethane and multi-functional reactive organic clay to considerably increase the thermo-tolerance and mechanical properties of polyurethane but reduce the water-absorption of polyurethane.
In Taiwanese Patent No. 261594, a method is disclosed for making dispersion of waterborne polyurethane/clay nanocomposites and its use in coating. Nanometer clay is modified by long alkyl or quaternary ammonium salt and used as a flame retardant, and mixed and polymerized with synthetic polyurethane to produce waterborne polyurethane with flame-retardant property. In addition, 50˜75 wt % of unmodified clay that is hydrophilic can be added into the waterborne polyurethane. Hydrophilic, suspended, stable, composite emulsion is flame-retardant, and the clay renders the coating more flame-retardant and increases the tensile strength of the coating without jeopardizing the adhesiveness of the emulsion.
In U.S. Pat. No. 6,203,901, disclosed are composite fibers and coating materials that include polyurethane resin and nanometer delaminated clay. The clay is modified by quaternary onium salts such as ammonium salts, phosphonium salts and sulphonium salts.
In U.S. Pat. No. 6,533,975, a method is disclosed to prepare nanocomposites and films that include polyurethane resin and delaminated clay. The polyurethane/clay dispersion is made of aprotic polar solvents such as dimethylacetamide by solution intercalation. Hence, nanometer laminated inorganic polymer composites increase mechanical strength, thermostability, flame-retardant ability, solvent-resistance and gas barrier ability.
None of the foregoing papers is focused on using reactive monomer with selective reactivity to modify organic/inorganic clay and using the modified clay to make clay/waterborne polyurethane composites. Hence, there is still room for improving the physical properties of waterborne polyurethane.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.